Thermoplastically processable, high-molecular, segmented, aromatic polycarbonate elastomers containing a variety of soft segments and their preparation processes are known (see, for example, U.S. Pat. No. 3,161,615, U.S. Pat. No. 3,030,335, U.S. Pat. No. 3,287,442, U.S. Pat. No. 3,189,662, U.S. Pat. No. 3,169,121, German Auslegeschrift 1,162,559, German Offenlegungsschrift 2,411,123, German Offenlegungsschrift 2,636,783, German Offenlegungsschrift 2,702,626, German Offenlegungsschrift 2,636,784, German Offenlegungsschrift 2,726,416, German Offenlegungsschrift 2,726,376, German Offenlegungsschrift 2,726,417, and German Patent Application P 28 27 325.
The products are thermoplastically processable and, because of their soft segments such as aliphatic polyethers, aliphatic polyesters, aliphatic polycarbonates or polysiloxanes, are characterized by their elasticity. The elasticity of these products depends on the ratio between the aromatic polycarbonate hard segments and the aliphatic soft segments such that the elasticity and elongation at break increase with the proportion of soft segment increase. These products also have a high heat distortion temperature resulting from the crystalline aromatic polycarbonate regions which impart to the polymer a high cross-linking density, even at relatively high temperatures. In addition, these polycarbonate elastomers can also be used to obtain products with a comparatively low heat distortion point resulting from a clear amorphous phase separation of the hard segment from the soft segment.
The disadvantage of almost all these products is that the aromatic polycarbonate hard segments, which impart to the polymer the high heat distortion temperature, do not form a separate phase sufficiently rapidly after thermoplastic processing and the products thus tend to stick to one another; the tackiness can be eliminated by additional processing steps such as, by subjecting the products to a heat treatment or to a drawing and a heat treatment after the thermoplastic processing. There is therefore a considerable expenditure of effort and expense associated with freeing these products from tackiness.
It has now been found, surprisingly, that aromatic polycarbonate elastomers which contain at least 5% by weight of co-condensed dimeric fatty acid esters as soft segments are no longer tacky after thermoplastic processing. It is particularly surprising that these products feature separate phases immediately after thermoplastic processing and are flexible also at low temperatures. Such controlled phase separation between the aromatic polycarbonate segments, based, for example, on bisphenol-A polycarbonate, and the polyester segment based on hexane-1,6-diol and dimeric fatty acid, while transparency is retained was hitherto unknown.
The preparation of polyester-polycarbonates from dimeric fatty acid, bisphenol A and phosgene by the pyridine process is in itself known and is described in U.S. Pat. No. 3,169,121, Example 17. The products according to that patent are built up only from dimeric fatty acid blocks with molecular weights of 560. In contrast, the polycarbonates, with co-condensed dimeric fatty acid esters, according to the present invention contain polyester blocks having molecular weights (number-average)Mn of 800 to 20,000, preferably 1,000 to 15,000 and in particular 2,000 to 10,000, and diols and are characterized by their separate phases. It is this critical feature which enables their use according to the invention.
The polycarbonates according to the invention containing at least 5% by weight of co-condensed dimeric fatty acid esters can be processed thermoplastically into transparent films, from which bags for packaging biological liquids and parenteral agents can be produced by heat impulse welding. These bags have a sufficiently high heat distortion temperature that they can be sterilized with steam in an autoclave at 121.degree. C.